Magnetic resonance imaging (MRI) entails generating an image of a region of interest based on spins excited by a pulse sequence and under the influence of a biasing magnetic field. Increasing the magnetic field strength holds promise of providing improved imaging and faster results. On the other hand, high field systems are very costly and medical care providers may tend to avoid using advanced MRI technologies as a cost saving measure.
In addition to pecuniary considerations, the interest in imaging using higher magnetic fields is frustrated by various factors, including limitations on specific absorption ratio (SAR) and current technology for ensuring a homogeneous magnetic field within the magnet bore.
Among the challenges associated with imaging at 10.5 T and higher are the B1+ inhomogeneities created by interference patterns due to the reduced wavelengths in the human body. The wavelengths of human tissue at the Larmor frequency (at 450 MHz for 10.5 T and 500 MHz at 11.7 T) are approximately 8 cm and 7 cm, respectively in high water content tissues such as muscle and brain. By conventional methods and thinking, these wavelengths would preclude any possibility of achieving safe and successful human-scale imaging.
Radio frequency (RF) interference patterns from conventional, uniform field volume arrays create severe RF field inhomogeneity in the anatomy. RF losses to the tissue may result in excessive heating when conventional pulse protocols are used.